The present invention relates to wireless communication systems and, in particular, the selective sizing of data blocks for wireless transport of data in an efficient manner.
Radio interfaces such as those proposed by the 3rd Generation Partnership Project (3G) use Transport Channels (TrCHs) for transfer of user data and signaling between User Equipment (UE), such as a Mobile Terminal (MT), and a Base Station (BS) or other device within node of a communication network. In 3G Time Division Duplex (TDD), TrCHs are a composite of one or more physical channels defined by mutually exclusive physical resources. TrCH data is transferred in sequential groups of Transport Blocks (TBs) defined as Transport Block Sets (TBSs). Each TBS is transmitted in a given Transmission Time Interval (TTI). User Equipment (UE) and Base Station (BS) physical reception of TrCHs require knowledge of Transport Block (TB) sizes.
For each TrCH, a Transport Format Set (TFS) is specified containing Transport Formats (TFs). Each TF, defines a TBS composed of a specified number of TBs where each TB preferably has the same size within a given TBS. Thus, a finite number of potential TB sizes are defined with respect to each TrCH.
Radio Resource Control (RRC) signaling is required between the BS and UE to define the attributes of each established TrCH, including a list of potential TB sizes. Signaling over the radio interface introduces system overhead, which reduces the physical resources available for user data transmission. Therefore, it is important to minimize RRC signaling and the number of potential TrCH TB sizes respectively.
All data transferred by specific TrCHs must fit into the TB sizes specified for the TFS of a particular TrCH. However, variable size data blocks exist that can not be predicted, for Radio Access Network (RAN) and Core Network (CN) signaling data, as well as Non-Real Time (NRT) user data transmissions.
To allow for the transfer of variable size data blocks, a Radio Link Control (RLC) provides a segmentation and re-assembly multiplexing function and a padding function. The segmentation and re-assembly multiplexing function reduces the size prior to transmission RLC and is used when the transferred data block is larger then the maximum allowed TB size. The padding function increases the data block or segmented data block size by padding with extra bits to fit a TB size.
Segmentation and re-assembly of data over more than one TTI is permitted for some, but not all, types of data. In 3G, it is not permitted, for example, for Common Control Channel (CCCH) logical data. Thus, the payload requirements for a TrCH carrying logical CCCH data are inherently restricted.
The RLC processing results in blocks of data are called Protocol Data Units (PDUs). A certain amount of each RLC PDU is required for control information. Using a relatively small RLC PDU results in a lower transfer data to control information ratio consequently resulting in a less efficient use of radio resources. The RLC padding function is used when the transferred data block is not equal to any of the allowed TB sizes. Likewise, the greater the difference between the transferred data block size and the next larger allowed TB size results in lowering the transfer data to used physical resources ratio consequently resulting in a less efficient use of radio resources. Therefore, it is important to maximize the number of potential TB sizes.
Lowering the number of TB sizes reduces RRC signaling overhead and increases radio interface efficiency. Increasing the number of TB sizes reduces RLC overhead and increases radio interface efficiency. It is therefore important to make the best use of the specified TB sizes for each TrCH.
TB sizes are the sum of the RLC PDU size and a Medium Access Control (MAC) header size. The MAC header size is dependent of the class of traffic, which is indicated by the Logical Channel type. A Target Channel Type Field (TCTF) is provided in the MAC header to indicate to which logical channel a TB is assigned. A TrCH can support multiple logical channel types. This means that the finite number of allowed TB sizes must support several MAC header sizes.
For RAN and CN signaling data and NRT user data, the RLC generates octet aligned (8 bit quantities) PDU sizes. Thus, the RLC PDUs are defined as groups of a selected number of octets, such that the RLC PDU bit size is always evenly divided by eight, i.e. the RLC PDU bit size always equals 0 modulo 8. This characteristic is maintained even when padding is required.
Applicant has recognized that, if MAC header sizes for different Logical Channel types have mutually exclusive bit offsets, TB sizes can not be generically used for all transmissions. TB sizes have to be defined for specific MAC headers and logical channels respectively. This increases signaling overhead and reduces RLC PDU size options, which results in less efficient use of radio resources.
Specifying octet aligned MAC header sizes as is currently done in some 3rd generation systems allows for some sharing of TB sizes between different Logical Channel types, but also increases MAC signaling overhead since the MAC header size must be at least 8 bits in such situations. In 3rd generation TDD mode, certain TrCH and Logical Channel combinations have very limited transfer block sizes and increasing MAC overhead should be avoided. Therefore, in TDD, TB size definitions are specific to Logical Channel specific MAC header bit offsets, and as described, reduces overall radio resource efficiency.
Applicant has recognized that without common MAC header bit offsets, it is not possible for MT down-link and BS up-link transmissions to octet align received frames in a physical layer since the bit offset is based on the logical channel type which cannot be known while at the physical layer. Therefore, TB""s have to be transferred to layer 2 for logical channel determination before bit shifting can occur. This means that considerable processing overhead is introduced for these TrCH""s. Applicant has recognized that with TrCH specific bit aligned MAC headers, bit shifting is known at the physical layer and no additional processing overhead is introduced.
A CDMA telecommunication system utilizes a plurality of protocol layers including a physical layer and a medium access control (MAC) layer such that the MAC layer provides data to the physical layer via plurality of transport channels (TrCHs). Each transport channel (TrCH) is associated with a set of logical channels for transporting logical channel data within transport channel data. At least one TrCH is associated with a set of logical channels having at least two logical channels of different types.
The physical layer receives blocks of data for transport such that the transport blocks (TBs) of data includes of a MAC header and logical channel data for one of the TrCHs. Each TB transports data for a given TrCH such that the logical channel data includes data associated with a selected logical channel from the set of logical channels associated with the given TrCH. Each TB has one of a selected limited finite number of TB bit sizes. The logical channel data for each TB has a bit size evenly divisible by a selected integer N greater than three (3). N is preferably eight (8) so that the logical data is in the form of an RLC PDU defined in terms of octets of data bits. Preferably the data manipulation and formatting is performed by one or more computer processors.
The MAC header for each TB includes data identifying the selected logical channel and has a bit size such that the MAC header bit size plus the logical channel data bit size equals one of the TB bit sizes. The MAC header bit size is fixed for TBs transporting data for the same TrCH and same selected logical channel, but may be different from the MAC header bit size for TBs transporting data for either a different TrCH or a different selected logical channel.
Preferably, for TrCHs associated with a set of multiple types of logical channels, a fixed MAC header bit size is associated with each logical channel within the set of logical channels and is selected such that each fixed MAC header bit size equals M modulo N where M is an integer greater than 0 and less than N. This results in a MAC header bit offset of M which is the same for all MAC headers associated with a given TrCH. This allows for a MAC header to be smaller than N in size. Thus, when N is 8, such as for octet aligned RLC PDUs, a MAC header can be smaller than one octet of data.
Preferably, each MAC header has a data field for data identifying the selected type of logical channel associated with the logical channel data. A bit size of that data field is preferably selected to determine the modulo N bit size of the MAC header, i.e. the MAC header bit offset. A shortest data field bit size is preferably provided for the data field of the MAC header of one or more logical channels of the set associated with the respective TrCH such that the logical channels designated by the shortest data field size are collectively more frequently used with the respective TrCH than any other logical channel within the associate set of logical channels. Alternatively, the shortest data field bit size may be associated with the most restricted TrCH logical channel combination payload requirement.
Preferably, the TrCHs includes a forward access channel (FACH) associated with a set of logical channels including a dedicated traffic channel (DTCH), a dedicated control channel (DCCH), a shared channel control channel (SHCCH), a common control channel (CCCH) and a common traffic channel (CTCH), and a random access channel (RACH) associated with a set of logical channels including the DTCH, the DCCH, the SHCCH and the CCCH. In such case, each MAC header preferably has a Target Channel Type Field (TCTF) for data identifying the selected logical channel type associated with the transport channel data where a bit size of the TCTF field is selected to determine the modulo N bit size M of the MAC header. The modulo N bit size M of the MAC header is preferably 3 modulo 8 for FACH and 2 modulo 8 for RACH.
The TCTF data field bit size is preferably 3 with respect to FACH MAC headers associated with the CCCH, CTCH, SHCCH and BCCH logical channels. The TCTF data field bit size is preferably 5 with respect to the FACH MAC headers associated with the DCCH and DTCH logical channels. The TCTF data field bit size is preferably 2 with respect to RACH MAC headers associated with the CCCH and SHCCH logical channels. The TCTF data field bit size is preferably 4 with respect to the RACH MAC headers associated with the DCCH and DTCH logical channels.
Other objects and advantages will be apparent to one of ordinary skill in the art from the following detailed description of a presently preferred embodiment of the invention.